1. Field of the Invention
The present invention relates to a rotor assembly for a dynamoelectric machine. In particular, this invention relates to a rotor assembly having a spider structure secured to a rotor shaft and a rotor rim structure. Still more particularly, this invention relates to a rotor assembly the supporting structure of which is exposed to large expansion forces due to rotation and/or temperature differences.
2. Description of the Prior Art
During the operation of a rotating electric machine the rotor rim is subject to strong centrifugal forces. It is therefore necessary to give the rotor assembly a construction which has sufficient dynamic stability at different speeds.
To this end, in previously used rotor assemblies the rotor rim has commonly been secured in such a manner that it is subjected to a high radial pre-stress, either by shrinking it on the rotor support structure or by loading it with radial pressure rods. Such a construction of the rotor assembly is, however, very expensive and demands great accuracy during manufacture and assembly.
In other previously used rotor assemblies a design has been applied which contains a rotor rim incorporating a magnetic core, a hub structure for securing a rotor shaft therein, and a center supporting structure or spider for connecting the rotor rim to the hub structure. In this design, dovetails are machined on the rotor spider arms and matching dovetail slots are punched into the more laminations of the rotor rim. The rotor core laminations are slid on the dovetail bars on the rotor spider arms, thus locking the rim to the arms and transmitting torque between the rotor rim and shaft. Such a design, however, does not allow for a free radial expansion of the rotor rim.
From various publications it is generally known to locate a rotor rim on a supporting structure or spider by means of guides, wedges or keys. These devices allow radial expansion but prevent angular motion between the punching of the rotor rim and the spider.
U.S. Pat. Nos. 3,046,426 and 3,470,405, for instance, both disclose a slot-and-key approach which allows a laminated rotor rim to move radially outward, but prevents peripheral movement relative to the spider structure. According to U.S. Pat. No. 3,046,426, a key or wedge can be used which is urged outwardly by a plate sandwiched between a pair of aligned spider arms. Grooves in the spider arms and in the lamination stack locate them with respect to one another, by means of the wedged core. In U.S. Pat. No. 3,470,404, basically the same design is used, although it applies multiple keys or wedges which ride in a separate channel formed by a U-shaped slide bar. In order to effect a favorable transmission of the tangential forces between the slide bars and the rotor disc, the slide bars are provided with tangentially protruding attachment members which are welded onto the ends of the web plates or arms of the spider. Yet, these members do not flex or bend outwardly.
In U.S. Pat. No. 1,687,512, a rotor assembly is disclosed which allows radial expansion of a laminated core or rim by means of locating pins which extend through the lamination and are received in mating holes of the spider. Thus, the connection between the spider arms and the rotor rim transmits torque between them without exerting radially acting forces which resist the outward movement of the rotor rim when its circumference elongates under the action of centrifugal forces. In particular, the pins are radially arranged and carried by the outer rim. They are slideably fitted in openings formed in angle brackets which are bolted to the ends of the spider arms. Also in this design a flexible connection between the spider arms and the rotor rim is not provided.
It is therefore an object of this invention to provide a rotor assembly that accommodates rotor rim expansion due to rotation and/or temperature differences while still allowing the rotor core to be located and supported in the stator core, and to transmit torque to or from the rotor shaft.
It is another object of this invention to provide a rotor assembly that permits small radial movements of the rotor rim in response to forces associated with rotation, while assuring that the rotor assembly will always remain concentric with its axis of rotation.
It is another object of this invention to provide a rotor assembly, including a spider or supporting structure for supporting the rotor rim, which permits a light and comparatively inexpensive construction for the supporting structure without overstressing the supporting construction due to radial movement of the rotor core in response to forces associated with rotation and different temperatures between the rotor rim and the supporting structure.
It is still another object of this invention to provide a simple manufacturing method for mounting a rotor rim on a supporting structure or spider in order to obtain a rotor assembly for a dynamoelectric machine.